| Abstract: | In accordance with the Montreal Protocol, production of all Halon fire suppressants ceased on 1 January 1994. FAR/JAR regulations require Halon 1211 or equivalent hand extinguishers to be installed on transport category aircraft. Although there is a Halon ’bank‘, a replacement agent will have to be found. The Aviation Authorities require that ’no loss of safety‘ should occur if a replacement agent is used. One proven benefit provided by Halon 1211 is the ability to extinguish hidden fires by a total flooding effect. Therefore, it is necessary to quantify the hidden fire-extinguishing ability exhibited by Halon 1211. Following an invitation for competitive tenders to develop a standard hidden fire test protocol, the Civil Aviation Authority (CAA) awarded a contract to Kidde International Research. After some range-finding work, a suitable test fixture was devised. This test fixture comprised arrays of four fires in two of five locations to establish in which regions an extinguishing concentration had been attained. A matrix of 10 tests ensured that each fire location was adequately represented. Tests have been carried out with hand extinguishers from four manufacturers. Results varied from 45% extinguishment to 60%, depending on the quantity of Halon contained in the extinguisher, and the discharge rate (a faster discharge rate creates more turbulence, aiding mixing and dispersion). In addition, tests were carried out using under- and over-filled extinguishers to examine the sensitivity of the test method. With the exception of one hand extinguisher, all results could be correlated to the mass and mass flow rate of agent used. This device extinguished a significantly higher percentage of fires than would be expected, based on its mass/mass flow rate characteristics. Limited testing was carried out with six Halon replacements: FM-200, FE-25, CEA-4.10, CEA-6.14, FE-36 and Triodide, using apparatus designed to give a constant discharge time (10±1 s). The results obtained appeared to be similar to Halon 1211 (50±5% extinguishment), provided the quantity of agent is scaled according to its n-heptane cupburner concentration. The two exceptions are agents with markedly different volatilities to Halon 1211 (b.p.−4°C): FE-25, b.p. −49° C, (65% extinguishment) and CEA-6.14, b.p.+58°C (35% extinguishment). Implications for the size and weight of a hand extinguisher, based on the results of these tests, are for the physically acting agents, a weight penalty of 1.4 to 2.6, and a volume penalty of 1.9 to 2.9. If Triodide is considered, there is a weight penalty of 1.06, and no volume penalty. However, it should be borne in mind that any hand extinguisher, before it is evaluated against hidden files, will have had to have passed the traditional ratings (currently UL 5B:C, BS 3A:34B) to be approved for aviation use. © 1997 John Wiley & Sons Ltd. |
